EP1072906B1 - Elément optique diffractif - Google Patents

Elément optique diffractif Download PDF

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Publication number
EP1072906B1
EP1072906B1 EP00306401A EP00306401A EP1072906B1 EP 1072906 B1 EP1072906 B1 EP 1072906B1 EP 00306401 A EP00306401 A EP 00306401A EP 00306401 A EP00306401 A EP 00306401A EP 1072906 B1 EP1072906 B1 EP 1072906B1
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EP
European Patent Office
Prior art keywords
diffraction
grating
optical element
diffraction optical
portions
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EP00306401A
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German (de)
English (en)
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EP1072906A2 (fr
EP1072906A3 (fr
Inventor
Takehiko c/o Canon K.K. Nakai
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Canon Inc
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Canon Inc
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
    • G02B27/0037—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration with diffracting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
    • G02B27/4211—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant correcting chromatic aberrations
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
    • G02B27/4216—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant correcting geometrical aberrations
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4272—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path
    • G02B27/4277—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path being separated by an air space
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1876—Diffractive Fresnel lenses; Zone plates; Kinoforms
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1876—Diffractive Fresnel lenses; Zone plates; Kinoforms
    • G02B5/189—Structurally combined with optical elements not having diffractive power
    • G02B5/1895—Structurally combined with optical elements not having diffractive power such optical elements having dioptric power

Definitions

  • This invention relates to a diffraction optical element, and particularly to a diffraction optical element suitable for use in a light including a plurality of wavelengths, or a wide-band light, and an optical system using the same.
  • a method of providing a diffraction optical element (hereinafter referred to also as the diffraction grating) having the diffracting action on a lens surface or a portion of an optical system to thereby decrease chromatic aberration is disclosed in literature such as SPIE, Vol. 1354, International Lens Design Conference (1990 ), Japanese Patent Application Laid-Open No. 4-213421 , Japanese Patent Application Laid-Open No. 6-324262 and U.S. Patent No. 5,044,706 .
  • This method utilizes the physical phenomenon that in a refracting surface and a diffracting surface in an optical system, chromatic aberration for rays of light of a certain reference wavelength appears in opposite directions. Further, such a diffraction optical element can also be given an effect like that of an aspherical lens by the period of the periodic structure thereof being changed, and has a great effect in reducing aberrations.
  • a ray of light is a ray of light still after refraction, whereas in diffraction, a ray of light is divided into a plurality of orders.
  • a diffraction optical element is used as a lens system, it is necessary to determine the grating structure so that a light beam of a wavelength area used may concentrate in a particular order (hereinafter referred to also as the "design order").
  • the design order the intensity of the other rays of diffracted light becomes low, and when the intensity is zero, the diffracted light thereof becomes null.
  • a diffraction optical element 201 having a diffraction grating 204 comprising a layer provided on a substrate 202 as shown in Fig. 16 of the accompanying drawings is formed on a certain surface
  • the characteristic of diffraction efficiency for the particular diffraction order is shown in Fig. 17 of the accompanying drawings.
  • the value of the diffraction efficiency is the rate of the quantity of each diffracted light to the whole transmitted light beam, and is a value in which the reflected light or the like on the boundary surface of the diffraction grating is not taken into consideration because it is complex to describe.
  • the axis of abscissas represents wavelength and the axis of ordinates represents diffraction efficiency.
  • the diffraction optical element 201 is designed such that in the first diffraction order (solid line in the figure), the diffraction efficiency becomes highest for the wavelength area used. That is, the design order is the first order. Further, the diffraction efficiency for the diffraction orders in the vicinity of the design order (zero order and second order which are first order ⁇ one order) is also shown. At the design order, the diffraction efficiency becomes highest for a certain wavelength (hereinafter referred to as the "design wavelength") and gradually becomes lower for the other wavelengths.
  • the decrement in the diffraction efficiency at this design order is the increment in the diffraction efficiency at the other orders than the design order, and diffracted lights of the other orders than the design order become flare lights. Also, when a plurality of diffraction optical elements are used, particularly a reduction in the diffraction efficiency at the other wavelengths than the design wavelength also leads to a reduction in transmittance.
  • Fig. 20 of the accompanying drawings shows the construction presented in the above-mentioned proposition, and it has a laminated cross-sectional shape in which two layers are stacked. High diffraction efficiency is realized by optimizing the refractive indices of materials forming the two layers, the spectral characteristic and the thickness of each grating.
  • a diffraction optical element is provided in an optical system, light beams of various angles of views usually enter the diffraction optical element. Therefore, if a diffraction optical element having a diffraction grating provided on a flat plate is used in an optical system, the angle of incidence of a light beam onto the diffraction optical element is changed by the angles of view, and the diffraction efficiency of diffracted light at the design order comes to be changed by the angles of view.
  • a laminated diffraction optical element as compared with the prior-art single-layer diffraction optical element shown in Fig. 16, tends to become greater in the thickness of the grating. Therefore, a laminated diffraction optical element formed on a flat plate, when used in an optical system having an angle of view, has its diffraction efficiency greatly reduced by the eclipse or the like of a light beam on the edge surface of the grating.
  • a diffraction optical element having a diffraction grating on a curved surface in an optical system having an angle of view.
  • a change in the angle of incidence of a light beam onto the diffraction optical element may be reduced depending on a change in the angle of view by the diffraction grating being provided on a curved surface which is concave relative to the stop.
  • EP-A-0902304 describes a diffractive optical element having diffraction grating surfaces which are formed with a small grating thickness as compared with the grating pitch.
  • EP-A-0902304 mentions that the diffraction grating could be formed on a curved lens surface.
  • US 5,076,684 discusses a multifocal ophthalmic lens having a diffractive zone plate formed on one side of the lens, the diffractive zone plate having a series of stepped diffractive zones.
  • EP-A-0965864 which was filed before the filing date of the present application but published after the filing date of the present application and therefore is only relevant when assessing the novelty of the claims of this application, discusses a diffractive optical element having a plurality of diffraction gratings. The edges of at least part of corresponding grating portions of the plurality of diffraction gratings are shifted from each other in a direction of arrangement of grating portions of each diffraction grating.
  • the present invention has as its object the provision of a diffraction optical element which, even when used in an optical system having an angle of view, has a small change in diffraction efficiency depending on the angle of view, and an optical system using the same.
  • Fig. 1 is a front view and a side view of the essential portions of the diffraction optical element
  • Figs. 2 and 6 are partial cross-sectional views of the element 1 of Fig. 1 along the line 2-2 of Fig. 1.
  • reference numeral 1 designates a diffraction optical element comprising the diffraction grating 6 of a first diffraction optical element 2 and the diffraction grating 7 of a second diffraction optical element 3 which are proximate and opposed to each other.
  • the diffraction gratings 6 and 7 constituting the diffraction optical element 1 comprise concentric circular grating shapes and have lens action.
  • the two adjacent diffraction gratings 6 and 7 provide curved surfaces (curved tip planes) 9 and 10 when the tips 6b (7b) of grating portions 6-1 (7-1) are ranged.
  • the two curved tip planes 9 and 10 are of equal curved surface shapes. O denotes an optical axis.
  • Fig. 2 is a view of the diffraction gratings 6 and 7 considerably deformed in the direction of depth of the gratings.
  • the diffraction optical element 1 is of a construction in which the first diffraction optical element 2 having the diffraction grating 6 formed on the surface of a substrate 4 and the second diffraction optical element 3 having the diffraction grating 7 formed on the surface of a substrate 5 are proximate to each other with air 8 therebetween. Further, the surfaces of the substrates 4 and 5 on which the diffraction gratings 6 and 7 are formed and the surfaces opposite thereto are curved surfaces, and the substrates 4 and 5 themselves have the action as a refracting lens.
  • the reference numerals 9 and 10 designate the curved tip planes of the diffraction gratings 6 and 7.
  • the diffraction efficiency of the diffraction optical element will first be described.
  • Fig. 17 shows the diffraction efficiency of the diffraction optical element 201 at this time.
  • the reference numerals 304 and 305 designate substrates
  • the reference numeral 308 denotes an air layer.
  • n 01 represents the refractive index of the material of the first diffraction grating 306 at the wavelength ⁇ 0
  • n 02 represents the refractive index of the material of the second diffraction grating 307 at the wavelength ⁇ 0
  • d1 and d2 represent the grating thickness of the first diffraction grating 306 and the second diffraction grating 307, respectively.
  • the signs of increase and decrease in each layer in expression (2) become such that the case of a grating shape (in the figure, the diffraction grating 307) in which as shown, the grating thickness increases from up to down is positive, and the case of a grating shape (in the figure, the diffraction grating 306) in which conversely, the grating thickness increases from down to up is negative.
  • a specific example will hereinafter be cited and described.
  • the following construction is adopted as the second diffraction optical element 303.
  • the diffraction efficiency of the first order diffracted light and zero order and second order in the vicinity thereof in this construction is shown in Fig. 22.
  • the first order diffracted light maintains high diffraction efficiency in the entire visible range. It can also be seen that the diffraction efficiency of the zero order and second order diffracted lights which are the neighboring orders of the first order diffracted light which is the design order is greatly reduced as compared with the example of the prior art shown in Fig. 17.
  • the diffraction optical element of the present invention having a diffraction grating formed on a curved surface.
  • the above-mentioned diffraction grating is formed on a curved surface having a radius of curvature R (hereinafter referred to as the reference curved surface).
  • the grating pitch of the diffraction grating when formed on a curved surface it is preferable that the grating pitch distributions at the positions of the tips 6b and 7b of those grating portions 6-1 and 7-1 of the diffraction gratings 6 and 7 adjacent to each other which are most proximate become substantially equal to each other. That is, design is made such that a segment linking the tips 6b and 7b of the grating portions 6-1 and 7-1 opposed to each other is substantially parallel to the optical axis O. Fig.
  • FIG. 4 shows as a comparative example a diffraction optical element of such a combination in which only the grating pitch distributions at the positions of the tips of the gratings on the substrate side (in Fig. 4, the groove bottoms 6c and 7c of the grating portions of the diffraction gratings 6 and 7) are equal to each other.
  • the diffraction gratings are shown and particularly the substrate is not shown.
  • a light beam propagating through an area represented by hatching A emerges from the grating portion 6-1 of the first diffraction grating 6, whereafter it does not enter a corresponding grating portion 7-1, but enters a grating portion 7-2 adjacent to this grating portion 7-1. Accordingly, the light beam in the area of hatching A cannot obtain a desired optical light path length difference and is not converted into diffracted light of the design order, but becomes unnecessary diffracted light of other order than the design order. Therefore, in the present embodiment, in order to reduce this unnecessary light beam, design is made such that as shown in Fig.
  • the grating pitch distribution at the position P of the tip of the grating most proximate to the grating portion 7-1 of the grating 7 adjacent to the grating portion 6-1 becomes equal to the grating pitch distribution at the position of the tip of the grating portion 6-1.
  • the shapes of the surfaces (curved tip planes) 9 and 10 in which the tips 6b and 7b of the grating portions 6-1 and 7-1 of the two adjacent diffraction gratings 6 and 7, respectively, are ranged are substantially equal to each other.
  • Fig. 5 shows as a comparative example a diffraction optical element 51 in which the shapes of only curved surfaces 4a and 5a in which the groove bottoms 6c and 7c of grating portions 6-1 and 7-1, respectively, are ranged are equal to each other.
  • a case where diffraction gratings 6 and 7 are formed on curved surfaces 4a and 5a of a radius of curvature R will be described as an example.
  • the radii of curvature of curved tip planes 4b and 5b in which the tips 6b and 7b of the grating portions 6-1 and 7-1 of the diffraction gratings 6 and 7 are ranged change by an amount corresponding to the thickness of the grating, and the radius of curvature of the curved tip plane 4b of the first diffraction optical element 2 is R-dl, and the radius of curvature of the curved tip plane 5b of the second diffraction optical element 3 is R+d2.
  • the spacing on the optical axis O between the curved tip planes 4b and 5b in which the tips 6b and 7b are ranged is defined as D1.
  • This fluctuation of the spacing is an amount which cannot be neglected when it is taken into account that the thickness of the grating is of the order of several ⁇ m.
  • the shapes of the curved tip planes 9 and 10 in which the tips 6b and 7b of the grating portions 6-1 and 7-1 of the two adjacent diffraction gratings 6 and 7 are ranged are made substantially equal to each other as shown in Figs. 2 and 6 (in Fig. 6, the both curved tip planes have the same radius of curvature R).
  • a diffraction optical element 70 is comprised of first, second and third diffraction optical elements 71, 72 and 73, design is made such that a curved tip plane 71c in which the tips 71b of the grating portions 71a-1 of the diffraction gratings 71a of the element 71 are ranged and a groove bottom curved surface 72c in which the groove bottoms 72d of the grating portions 72a-1 of the diffraction gratings 72a of the element 72 adjacent to the element 71 are ranged are made into curved surfaces (radius of curvature R) equal in radius of curvature to each other.
  • curved tip planes 72d and 73c in which the tips 72e and 73b of the grating portions 72a-1 and 73a-1 of the adjacent diffraction gratings 72a and 73a are ranged become curved surfaces (radius of curvature R-d2) equal in radius of curvature to each other.
  • R-d2 radius of curvature
  • a curved surface 12 having a desired radius of curvature R is imaginarily disposed at the intermediate position of the spacing D1 between the grating tips facing each other.
  • the radius of curvature of the first diffraction grating 6 is defined as R+D1/2
  • the radius of curvature of the second diffraction grating 7 is defined as R-D1/2.
  • the grating edge position (zonal radial position) is determined so as to satisfy a desired diffraction condition on the aforementioned imaginary curved surface R.
  • a conical surface perpendicularly intersecting with the imaginary curved surface R at this position is generated, and positions at which this conical surface intersects with the curved tip planes 9 and 10 in which the grating tips of the mountain sides of the respective grating portions are ranged are defined as the grating edge positions of the respective diffraction optical elements.
  • This construction is a construction in which the spacing between the grating portions is kept at a constant value D1 in a direction perpendicularly intersecting with the reference curved surface and the grating edge positions of the respective grating portions are made coincident with each other.
  • proximate grating tips of the two adjacent grating portions 7-1 and 7-2 are of the same grating pitch distribution and the curved tip planes 9 and 10 in which the grating tips of the respective grating portions are ranged are the same curved surfaces
  • the construction shown in Fig. 8 is preferable, but when the spacing D1 between the grating portions is as small as 1-3 ⁇ m, there is no great difference between the two, and from the ease of manufacture, the construction shown in Fig. 2 is preferable.
  • each diffraction grating will now be described. As shown in Fig. 9, design is made such that the angle ⁇ formed by the grating edge portions 11a and 11b with respect to the grating surface 6a becomes the same (the edge portion 11a) as or more obtuse (the edge portion 11b) than the angle ⁇ formed between a surface normal 11c at a point whereat the curved tip plane 9 and the grating tip 6b intersect with each other and the grating surface 6a, that is, ⁇ ⁇ ⁇ .
  • a diffraction optical element with the productivity thereof taken into account, is often made by plastic molding or ultraviolet ray setting resin molding by the use of a mold.
  • a molded article having a curved surface shape is generally said to shrink in the direction of a plane perpendicular to the curved surface, and from this, it is preferable to form the grating edge portions 11a and 11b as described previously in order to mold the grating portions with good parting.
  • grating thickness d1 (d2) of each diffraction grating will now be described.
  • design is made such that as shown in Fig. 2, a grating thickness projective component in the direction of a surface normal 11c at a position whereat the curved tip planes 9 and 10 in which the tips of the grating portions are ranged and the grating tips 6b and 7b intersect with each other becomes constant. That is, design is made such that the lengths of the grating edge portions 11a and 11b in a direction parallel to the surface normal become constant.
  • Fig. 10 shows as a comparative example the cross-sectional shape of a diffraction grating in which the grating thickness parallel to the optical axis O is constant.
  • the cross-sectional shape shown in Fig. 10 is a grating condition under which there is obtained optimum diffraction efficiency when a light beam entering the diffraction optical element enters substantially in parallelism to the optical axis O.
  • the grating edge portions 11a and 11b are formed perpendicularly to the reference curved surface R, those of parallel light beams which are indicated by A1 and A2 enter the grating edge portions 11a and 11b, and become unnecessary light beams which are not diffracted in a desired direction of diffraction. Accordingly, to reduce the influence of these unnecessary diffracted lights, it is preferable to use the diffraction optical element so that the light beams may enter the reference curved surface substantially perpendicularly thereto. At this time, the phase difference the diffraction optical element gives to the incident light beams is given from the difference in the length of the optical light path through which the light beams pass.
  • the length (ab) of the edge portion 11a in the direction of the optical axis O becomes the grating thickness dab and this is a small grating thickness as compared with the desired grating thickness d1. Therefore, as in the embodiment of the present invention shown in Fig. 2, design is made such that the grating thickness component in the direction of the surface normal 11c of the curved surfaces 9 and 10 at a position whereat the curved tip planes 9 and 10 in which the tips of the grating portions are ranged and the tips of the grating portions intersect with each other becomes constant, whereby optimum diffraction efficiency is obtained in the use of a diffraction optical element in which the influence of the grating edges is small.
  • Fig. 3 shows the diffraction efficiency of the diffracted light of the design order of the light beam which has entered the diffraction optical element of the embodiment of the present invention from the direction of a perpendicular to the curved tip planes, and the diffraction efficiency of the diffracted light of the design order of the light beam which has entered the diffraction optical element shown in Fig. 10 from the direction of the optical axis O.
  • the grating pitch is 70 ⁇ m
  • the angle formed by and between the surface normal of the reference curved surface and the optical axis is 5°
  • the grating thickness d1 satisfies 6.9 ⁇ m
  • the grating thickness d2 satisfies 9.5 ⁇ m.
  • solid line (2) indicates the diffraction optical element of the embodiment of the present invention
  • dotted line (1) indicates the diffraction optical element of the construction of Fig. 10.
  • Fig. 12 is a schematic view of the essential portions of Embodiment 2 of the diffraction optical element of the present invention.
  • Embodiment 1 has been of a construction in which the first and second diffraction optical elements are disposed in proximity to each other.
  • Example 2 adopts a construction as shown in Fig. 12 wherein two diffraction optical elements 2 and 3 are adhesively secured to each other in a non-grating area 13 in which the diffraction gratings of the diffraction optical elements 2 and 3 are absent.
  • the adherence of dust to the surfaces of the gratings can be greatly reduced if the elements are assembled up to the adhesive securing in an environment such as a clean room wherein little dust is present. Also, after the adhesive securing, the surfaces of the gratings are not touched and therefore, the working property when the diffraction optical element 1 is incorporated into other optical system is greatly improved.
  • Fig. 13 is a schematic view of the essential portions of Example 3 of the diffraction optical element of the present invention.
  • the diffraction optical elements of the aforedescribed Examples 1 and 2 are of a aforedescribed Examples 1 and 2 are of a construction in which two diffraction gratings are disposed in proximity to each other.
  • the relative position between the two diffraction gratings may three-dimensionally cause an error.
  • portions 14 for regulating the spacing between the grating portions in the direction of height thereof are provided in non-grating areas 13, whereby the relative spacing between the grating portions in the direction of depth thereof is provided with good accuracy.
  • the alignment of the diffraction gratings may be accomplished by effecting the alignment only in xy directions and the working property is greatly improved. Also, the problem that during alignment, the diffraction gratings interfere with each other and the tips of the gratings are deformed is eliminated. If the portions 14 for regulating the height of the grating portions in the present embodiment are integrally formed of the same material as the material of the diffraction gratings 6 and 7 when the diffraction gratings 6 and 7 are prepared, it will be preferable in both of accuracy and cost. Further, when as shown in Figs. 1, 12 and 13, the substrate has a lens shape, if such adjustment that the relative eccentricity of two lenses is offset is carried out during alignment adjustment, there can be provided a diffraction optical element of good performance in which transmission optical eccentricity is little.
  • Example 4 of the diffraction optical element of the present invention will now be described.
  • the materials forming the substrate and the diffraction gratings differ from each other, this is not restrictive, but the material forming the diffraction gratings may be the same as the material of the substrate and the diffraction gratings may be manufactured integrally with the substrate.
  • the outer diameter of the substrate and the positions of the centers of the diffraction gratings can be adjusted with good accuracy. Or when the substrate has a lens shape, it becomes possible to adjust the core of the substrate lens and the centers of the gratings well. Accordingly, the optical axis adjusting accuracy when the diffraction optical element of the present invention is incorporated into other lens is improved, and the deterioration of an aberration such as imaging performance caused by the element becoming eccentric can be greatly reduced.
  • Fig. 14 is a schematic view of the essential portions of an optical system using the diffraction optical element according to the present invention.
  • Fig. 14 shows a cross-section of the photo-taking optical system of a camera or the like
  • the reference numeral 101 designates a photo-taking lens having a stop 102 and one of the aforedescribed several diffraction optical elements 1 therein.
  • the reference numeral 103 denotes film or a CCD which is an imaging surface.
  • the diffraction optical element according to the present invention By using the diffraction optical element according to the present invention, the wavelength dependency of diffraction efficiency is greatly improved and therefore, there can be obtained a photo-taking lens of high performance in which flare is little and the resolving power at low frequencies is high. Also, this diffraction optical element can be prepared by a simple manufacturing method and therefore, an inexpensive optical system excellent in mass productivity as a photo-taking optical system can be provided.
  • the diffraction optical element 1 of the present invention is provided on the cemented surface of the fore lens, this is not restrictive, but the element 1 may be provided on the surface of the lens, or a plurality of diffraction optical elements according to the present invention may be used in the photo-taking lens.
  • the diffraction optical element of the present invention can also be used in various imaging optical systems used in a wide wavelength range, such as the photo-taking lens of a video camera, the image scanner of a business machine and the reader lens of a digital copier to thereby obtain a similar effect.
  • Fig. 15 is a schematic view of the essential portions of an optical system using the diffraction optical element according to the present invention.
  • Fig. 15 shows a cross-section of the observation optical system of binoculars or the like
  • the reference numeral 1 designates an objective lens including one of the diffraction optical elements of the aforedescribed embodiments
  • the reference numeral 104 denotes image reversing means such as a poroprism for forming an image
  • Fig. 15 it is shown as a glass block for the sake of simplicity.
  • the reference numeral 105 designates an eyepiece
  • the reference numeral 106 denotes an evaluation plane (pupil plane).
  • the diffraction optical element 1 is formed with a view to correct the chromatic aberration or the like on the imaging plane 103 of the objective lens.
  • the diffraction optical element according to the present invention By using the diffraction optical element according to the present invention, the wavelength dependency of diffraction efficiency is greatly improved and therefore, there can be obtained an objective lens of high performance in which flare is little and the resolving power at low frequencies is high. Also, the diffraction optical element of the present invention can be prepared by a simple manufacturing method and therefore, there can be provided an inexpensive optical system excellent in mass productivity as an observation optical system.
  • the diffraction optical element is formed on the objective lens portion, this is not restrictive, but a similar effect may be obtained even if the diffraction optical element is formed on the surface of the prism or at a position in the eyepiece.
  • the diffraction optical element being provided more adjacent to the object side than the imaging plane, there is the chromatic aberration reducing effect by only the objective lens and therefore, in the case of an observation system for the naked eye, it is desirable to provide the diffraction optical element at least on the objective lens side.
  • the optical system of the present embodiment has been shown as binoculars, whereas this is not restrictive, but it may be an optical system such as a ground telescope or an astronomical telescope, and the present invention can also be applied to an optical system such as the optical type finder of a lens shutter camera, a video camera or the like to thereby obtain an effect similar to that in the case of binoculars.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Claims (10)

  1. Elément optique (1) de diffraction ayant plusieurs réseaux (6,7) de diffraction alignés suivant un axe optique commun et comprenant deux réseaux de diffraction formés de matières respectives différentes ayant des dispersions différentes, l'élément optique (1) de diffraction comportant :
    un premier réseau (6) de diffraction ayant un premier groupement de parties de réseau, chaque partie de réseau du premier groupement de parties de réseau ayant une pointe (6b) ; et
    un second réseau (7) de diffraction ayant un second groupement de parties de réseau, chaque partie de réseau du second groupement de parties de réseau ayant une pointe (7b),
    dans lequel les pointes (6b) du premier groupement de parties de réseau définissent une première surface courbe imaginaire (9) et les pointes (7b) du second groupement de parties de réseau définissent une second surface courbe imaginaire (10) qui est concentrique à la première surface courbe imaginaire (9) et séparée de la première surface courbe imaginaire (9), et
    caractérisé en ce que, sur une zone d'utilisation, une ligne reliant une pointe (6b) du premier groupement de parties de réseau à une pointe correspondante (7b) du second groupement de parties de réseau est perpendiculaire aux première et seconde surfaces courbes imaginaires (9, 10).
  2. Elément optique de diffraction selon la revendication 1, dans lequel les premier et second réseaux de diffraction (6,7) sont séparés par une couche d'air.
  3. Elément optique de diffraction selon la revendication 1 ou la revendication 2, dans lequel les premier et second réseaux (6,7) de diffraction sont fixés l'un par rapport à l'autre par l'intermédiaire d'une zone (13) sans réseau de l'élément optique (1) de diffraction.
  4. Elément optique de diffraction selon l'une quelconque des revendications précédentes, pouvant être mis en oeuvre pour une utilisation dans une plage visible de longueurs d'onde.
  5. Elément optique de diffraction selon l'une quelconque des revendications précédentes, comportant en outre un substrat sur lequel au moins certains des multiples réseaux de diffraction sont situés, la matière d'au moins l'un des multiples réseaux de diffraction étant identique à la matière du substrat.
  6. Elément optique de diffraction selon la revendication 5, dans lequel le substrat a une action de lentille.
  7. Elément optique de diffraction selon l'une quelconque des revendications précédentes, formé sur la surface collée d'une lentille collée.
  8. Système optique comportant un élément optique de diffraction selon l'une quelconque des revendications précédentes.
  9. Système optique selon la revendication 8, lequel système optique est un système optique de formation d'image.
  10. Système optique selon la revendication 8, lequel système optique est un système optique d'observation.
EP00306401A 1999-07-28 2000-07-27 Elément optique diffractif Expired - Lifetime EP1072906B1 (fr)

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EP1072906A2 (fr) 2001-01-31
EP1072906A3 (fr) 2003-05-28
US6829093B1 (en) 2004-12-07
DE60035834T2 (de) 2008-04-30
DE60035834D1 (de) 2007-09-20
JP2001042112A (ja) 2001-02-16

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